Re: [PATCH] POWER9 PMU interrupt after idle workaround

[Madhavan Srinivasan <maddy@linux.vnet.ibm.com>]

On Monday 10 July 2017 11:49 AM, Nicholas Piggin wrote:
> POWER9 DD2 can see spurious PMU interrupts after state-loss idle in
> some conditions.
>
> A solution is to save and reload MMCR0 over state-loss idle.

Acked-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>

> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>   arch/powerpc/kernel/idle_book3s.S | 15 ++++++++++++++-
>   1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
> index 5adb390e773b..516ebef905c0 100644
> --- a/arch/powerpc/kernel/idle_book3s.S
> +++ b/arch/powerpc/kernel/idle_book3s.S
> @@ -30,6 +30,7 @@
>    * Use unused space in the interrupt stack to save and restore
>    * registers for winkle support.
>    */
> +#define _MMCR0	GPR0
>   #define _SDR1	GPR3
>   #define _PTCR	GPR3
>   #define _RPR	GPR4
> @@ -272,6 +273,14 @@ power_enter_stop:
>   	b 	pnv_wakeup_noloss
>
>   .Lhandle_esl_ec_set:
> +	/*
> +	 * POWER9 DD2 can incorrectly set PMAO when waking up after a
> +	 * state-loss idle. Saving and restoring MMCR0 over idle is a
> +	 * workaround.
> +	 */
> +	mfspr	r4,SPRN_MMCR0
> +	std	r4,_MMCR0(r1)
> +
>   /*
>    * Check if the requested state is a deep idle state.
>    */
> @@ -450,10 +459,14 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_ARCH_300)
>   pnv_restore_hyp_resource_arch300:
>   	/*
>   	 * Workaround for POWER9, if we lost resources, the ERAT
> -	 * might have been mixed up and needs flushing.
> +	 * might have been mixed up and needs flushing. We also need
> +	 * to reload MMCR0 (see comment above).
>   	 */
>   	blt	cr3,1f
>   	PPC_INVALIDATE_ERAT
> +	ld	r1,PACAR1(r13)
> +	ld	r4,_MMCR0(r1)
> +	mtspr	SPRN_MMCR0,r4
>   1:
>   	/*
>   	 * POWER ISA 3. Use PSSCR to determine if we